The research found women comprised 18% of all directors, executive producers, writers, cinematographers and editors.

It also showed women were more likely to work in the documentary, drama and animated film genres.

The Centre has been conducting the industry survey for more than a decade to track trends.

The number of female producers has held steady at 25% for the past two years, while female writers rose to 15%, up from a low of 10% in 2006.

The number of female editors between 1998-2012 has remained fairly constant in the 20%-21% range. Cinematographers have fluctuated between 2%-4%, although figures for 2012 were on the low end of the range.

No women have made it onto the shortlist for best director at this year's Oscars, while Zero Dark Thirty is the only best picture nominee to have been directed by a woman - Oscar-winner Kathryn Bigelow.

Looking at films shown at the Sundance Film Festival over the past decade - and accounting for 820 narrative and documentary films - researchers found women represented 29.8% of some 11,000 filmmakers.

There are more women working in documentary films than narrative films, but study director Stacy Smith said her research found that "as commerce moves in, females move out".

Women In Film president Cathy Schulman added: "This data shows us that there is a higher representation of female filmmakers in independent film as compared to Hollywood - but it also highlights the work that is still to be done for women to achieve equal footing in the field."

The study also found that films directed by women employ greater numbers of women behind the camera than those made by men.

The organisers of last year's Cannes Film Festival were criticised when the list of 22 films nominated for its top prize, the Palme d'Or, was entirely made up of male directors.